Alternating Electric Field-Assisted Matrix Nano-Coating for High Spatial Resolution MALDI Imaging

The simultaneous achievement of matrix nano-coating and efficient in situ enrichment of analytes is currently an important aspect affecting the ability of matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to efficiently explore endogenous compounds in situ with high-resolution. Herein, a novel matrix coating approach called alternating electric field-assisted matrix nano-coating (AEFAMnC) is reported, which is designed to amplify the capabilities of high-resolution MALDI imaging. The use of AEFAMnC achieves matrix nano-coating (the smallest crystal size, ca. 70 nm), resulting in superior uniform matrix deposition. Interestingly, AEFAMnC leverages asymmetric alternating electric fields to initiate a repetitive forced micro-extraction process, which significantly enhance the in situ enrichment of compounds on the sample surface for more adequate co-crystallization with the matrix. These features finally improve in situ ionization efficiency and high-resolution imaging performance of endogenous compounds across various biological samples (i.e., rat brain, germinating Chinese yew seeds, and single cells) at 5-µm pixel size. Overall, for the first time, AEFAMnC simultaneously achieves both matrix nano-coating and in situ repetitive forced micro-extraction of analytes, significantly improving the performance of high-spatial-resolution MALDI-MSI. AEFAMnC has far-reaching implications in high-resolution MALDI imaging, particularly in MS-based single-cell spatial omics studies.